Pre MOT check

Well the washers and wipers fine , next the lights all ok apart from one headlight ! I have been putting this off since I bought the Griff went out and got myself some axle stands and a trolley jack ,anyway took the light cover off all looked ok so took the bulb out and tested it on a PP9 and it came on ! if a little dim so off to Homebase to get a multimeter tested the earth to live and it shows about 11.6 volts ? so back to Halfrauds to get some new bulbs fitted the new bulb and you guessed it nought .
Not being an engineer or an electrician I'm stumped , any ideas gratefully received , Rgds Simon

I realise it will be dim on a 9v battery but the point is it lights up on the battery but 0 when in the car , and Ive not taken it to Halfrauds I just bought the bulbs from them ,well and the trolley jack and axle stands , Simon

Taking it to local garage I have used before , it didn't work with original bulb and not with new either , battery a bit low I presume because I keep checking the lights without the engine running and it still starts the engine fine so cant be that much wrong with it ,the battery that is ,Simon

Also, is it not working one side, or both?

You need to load the circuit while the volt meter is attached a digital volt meter wont do this solo that voltage is a tad low I would assume because you have resistance in the circuit (ground probably) I would be checking grounds but a quick test could be carried out running a temp ground to the 3 pin connector ground cable (easy to test) if it dont light on main beam either then the chances are its ground related

Thanks Sardonicas for your input , but what 3 pin connector , I just have a couple of spade connectors ? Rgds Simon